RE: [PATCH 2/3] KVM: nVMX: Fix fail to get nested ack intr's vector during nested vmexit

Zhang, Yang Z
2014-07-17T09:14:05Z

Paolo Bonzini wrote on 2014-07-17:
> Il 17/07/2014 06:56, Wanpeng Li ha scritto:
>> && nested_exit_intr_ack_set(vcpu)) {
>> int irq = kvm_cpu_get_interrupt(vcpu);
>> +
>> + if (irq < 0 && kvm_apic_vid_enabled(vcpu->kvm))
>> + irq = kvm_get_apic_interrupt(vcpu);
>
> There's something weird in this patch. If you "inline"
> kvm_cpu_get_interrupt, what you get is this:
>
> int irq;
> /* Beginning of kvm_cpu_get_interrupt... */
> if (!irqchip_in_kernel(v->kvm))
> irq = v->arch.interrupt.nr;
> else {
> irq = kvm_cpu_get_extint(v); /* PIC */
> if (!kvm_apic_vid_enabled(v->kvm) && irq == -1)
> irq = kvm_get_apic_interrupt(v); /* APIC */
> }
>
> /* kvm_cpu_get_interrupt done. */
> if (irq < 0 && kvm_apic_vid_enabled(vcpu->kvm))
> irq = kvm_get_apic_interrupt(vcpu);
>
> There are just two callers of kvm_cpu_get_interrupt, and the other is
> protected by kvm_cpu_has_injectable_intr so it won't be executed if
> virtual interrupt delivery is enabled. So you patch is effectively the same as this:
>
> diff --git a/arch/x86/kvm/irq.c b/arch/x86/kvm/irq.c index
> bd0da43..a1ec6a5 100644 --- a/arch/x86/kvm/irq.c +++
> b/arch/x86/kvm/irq.c @@ -108,7 +108,7 @@ int
> kvm_cpu_get_interrupt(struct kvm_vcpu *v)
>
> vector = kvm_cpu_get_extint(v);
> - if (kvm_apic_vid_enabled(v->kvm) || vector != -1)
> + if (vector != -1)
> return vector; /* PIC */
>
> return kvm_get_apic_interrupt(v); /* APIC */
> But in kvm_get_apic_interrupt I have just added this comment:
>
> /* Note that we never get here with APIC virtualization
> * enabled. */
>
> because kvm_get_apic_interrupt calls apic_set_isr, and apic_set_isr
> must never be called with APIC virtualization enabled either. With
> APIC virtualization enabled, isr_count is always 1, and
> highest_isr_cache is always -1, and apic_set_isr breaks both of these invariants.
>

You are right. kvm_lapic_find_highest_irr should be the right one.

> Paolo

Best regards,
Yang